The present invention relates to a continuous process for the manufacture of a non Newtonian paste or cream like material such as dentrice or a cosmetic.
Dentifrices such as toothpaste or dental creams are generally extrudible pastes which contain insoluble abrasives and/or polishing agents that are used in the removal of plaque, stains and other deposits from the teeth and also help in polishing the teeth.
In one well known method of manufacture of dentifrices the dentifrices during the manufacturing are subjected to high temperature and prolonged periods of vacuum. These conditions cause a loss of volatiles such as flavoring agents during the manufacturing process. The improved continuous process of the instant invention does not employ high temperatures and prolong periods of vacuum thereby minimizing the loss of volatiles as well as reducing the cost of manufacturing due to low energy input requirements. Additionally, the resultant compositions of the instant invention exhibit non-Newtonian flow characteristics have enhanced flavor, a G' value over a strain range of 0.1 to 0.5 percent at 6.3 radians/second of at least about 4,000 dynes/sq. cm. and a complex viscosity over a strain range of 0.1 to 5% at 6.3 radians/second of at least about 700 pascal seconds thereby exhibiting improved rheological properties and improved product stability.
Toothpaste can be made up by various and many well known techniques. One such technique is disclose U.S. Pat. No 3,840,657 issued Oct. 8, 1974, wherein a toothpaste composition is manufactured by making a mixture of a liquid vehicle, gelling agent and polishing agent; degassing this mixture; preparing a second mixture of a synthetic organic detergent and a liquid vehicle therefore, and degassing this mixture by raising it to a elevated temperature; and finally admixing the first and second mixtures. In the manufacture of toothpastes, invariably the powdered constituents must be mixed and dispersed with the other liquid ingredients contained in the final toothpaste product. Care must be taken to remove the air in the mixing in of the powders so as to prevent the entrainment of air in the resulting paste.
Various known methods are disclosed in such standard references as "Cosmetics: Science and Technology", by Sagarin, Volume I, pages 510-511, published by Interscience Publishers, Inc. (1972). One such method is the mixing of a paste mass under vacuum to remove the entrained air. The speed of removal will generally depend on the air quantity and mixer construction. Air can also be removed by atmospheric mixing followed by the use of a continuous deaerator such as a Versator available from Cornell Machine Co. The efficiency of deaeration will again be a function of the quantity of air present in the paste mass.
U.S Pat. No. 2,751,328 teaches a continuous or semi continuous process for the manufacture of toothpaste. The process of this patent teaches a method similar to the instant invention but differs in the means of forming the dental paste and cream in it requires the maintaining of the slurry of the components at a temperature in excess of 140.degree. F. up to 270.degree. F. for a residence time of 3.5 minutes with agitation. These conditions of the process of U.S. Pat. No. 2,751,328 because of the elevated temperature, residence time and agitation provide compositions which do not have improved G' values, increased complex viscosities, product stability, enhanced flavor or dispersion of the particles in the composition that are comparable to the compositions of the instant invention because of the incomplete formation of the polymeric matrix.
U.S. Pat. No. 4,599,363 describes a continuous process for the manufacture of dentifrices. Like the previously described batch processes and unlike the continuous process of the instant invention this patent describes a process that employees high temperature and prolong periods of vacuum.
Accordingly, the instant improved continuous process for the manufacture of dentifrices produces dentifrices having non-Newtonian flow characteristics, enhanced flavor, and having improved rheological properties of a G' value over a strain range of 0.1 to 0.5 percent at 6.3 radians/second of at least about 4000 dynes/sq. cm, more preferably at least about 5,000 dynes/sq.cm and most preferably at least about 5,500 dynes/sq. cm and a complex viscosity over a strain range of 0.1 to 0.5% at 6.3 radians/second of at least about 700 Pascal-seconds, more preferably at least 800 Pascal-seconds and most preferably at least about 900 Pascal-seconds.